Electrical resistor



July 3, 1951 M. A. THOM 2,558,798

' ELECTRICAL RESISTOR Filed Oct. 18, 1948 INVE'N TOR. j eZz/mflfZom mom,

Patented July 3, 1951 UNITED STATES PATENT OFFICE ELECTRICAL RESISTORMelvin A. Thom, Brighton, N. Y.

Application October 18, 1948, Serial No. 55,193

This invention relates to an electrical resistor, with particularreference to the type of unit including a wire resistance element woundupon a porcelain or another electrically insulating core, and it has forits purpose to afford a structure of small size that is compact andcapable of withstanding large electrical loads and high temperatureswithout fracture or excessive heating.

More particularly the invention has for its purpose to afford aconstruction that lends itself to being mounted on a metal chassis in asmall space, and so constructed that the heat generated by theresistance wire is easily and quickly dissipated.

A still further purpose of the invention is to afford an eflicient anddurable construction of practical and economical manufacture that isespecially useful for electronic installations in airplanes and otherapplications where conservation of space is highly essential and whereit is necessary for a resistor to have a high currentcarrying capacityso as to conduct such currents as may be required without the partsbecoming excessively heated or without causing fracture, damage,disintegration or lessening the efficiency of the resistor.

More specifically, the invention has for its purpose to provide ahousing of metal or other heatconducting material within which theresistor is mounted in such a way as to be effectively insulatedtherefrom electrically, the metal housing being attachable to a metalchassis or support and the resistor being mounted therein in such a wayas to conduct away and dissipate a large part of the heat generated bythe current passing through the resistance element, so that the surfacesof the metal housing and the surface of the metal chassis adjacent tothe housing do not become excessively heated, and the resistor isprotected from fracture or damage that might otherwise result fromelectrical overload or excessively high temperatures.

To these and other ends, the invention consists in the construction andarrangement of parts that will appear clearly from the followingdescription when read in conjunction with the accompanying drawings, thenovel features being pointed out in the claims following thespecification.

In the drawings:

Fig. 1 is a plan view of an electrical resistor constructed inaccordance with a preferred embodiment of the invention, and showing thehousing attached to a chassis or supporting plate;

3 Claims. (Cl. 201-67) Fig. 2 is a. view in side elevation of the same;

Fig. 3 is a vertical sectional view taken centrally of Fig. 1, and

Fig. 4 is a view in end elevation.

The invention is illustrated in connection with an electrical resistorof the type and construction disclosed in copending application Ser. No.31,236, filed June 5, 1948, now Patent #2,524,550, issued October 3,1950, which embodies a generally cylindrical electrical resistorincluding a wire resistance, not shown, and having an exterior contoursuch as shown in Fig. 3, including a cylindrical central portion I oflesser diameter, cylindrical end portions 2 of greater diameter, andconductors 3 extending centrally from the ends of the resistor, it beingunderstood that the resistor is covered with an electrically insulatingsilicone varnish, shellac, plastic, resin, or other suitable materialentirely surrounding the cylindrical surfaces of the resistor and itsends around the conductors 3, so that the porcelain core or body andinterior of the resistor is effectively sealed against moisture. I

Such a resistor is limited in the load it will carry depending on itssize, and in order to accommodate the maximum loads required, it isnecessary to employ much larger resistors than desirable in order toprevent excessive heating, fracture, or other damage. It is essentialand important to provide for greater heatdissipation than heretoforepossible in order to employ a resistor of small size while carryingmaximum electrical loads, and to accomplish the resistor is mountedwithin a housing of aluminum, or other metal or suitable heat-conductingmaterial, which is constructed for attachment to a metal chassis orsupport and acts to dissipate readily and effectively the heat generatedby any load towhich the resistor may be subjected.

Accordingly there is provided an integral, rigid housing of aluminum orother suitable metal or heat-conducting material, provided at its upperportion with a cylindrical longitudinally extending opening 4 withinwhich the resistor such as previously described, or other suitableresistor, is located, the housing preferably including a curved topaffording a relatively thin top wall 5 above surrounding the resistorand between it and the metal housing, such insulating material beingapplied in such a way as to avoid the possibility of any air pockets orvoids remaining in the spaces surrounding and between the resistor andhousing.

Such electrically insulating material preferably comprises a wovensleeve 1 of fiber glass or other suitable insulating material that ispositioned and fits snugly around thecentral portion 1 of the resistorbefore the latter is inserted into the metal housing, the flexible wovenglass sleeve 1 being cut of proper length to just fill the space aroundthe central portion 9 of the resistor, and the flexible glass sleeve Imay be temporarily held in place by winding a glass or other thread 8that will stand high temperature therearound, after which a flexibleinsulating sleeve 9 is fitted over the sleeve 1 and the enlarged ends 2of the resistor, the flexible sleeve 9 being also preferably of wovenfiber glass or other suitable efectrically insulating material and of asize to fit snugly around the sleeve '1 and ends of the resistor andapproximately the length of the resistor.

After the sleeves 'l and 9 are assembled, the resistor with the wovenfiber glass sleeves in position is dipped or the sleeves otherwisesaturated with resin varnish, plastic, or other electrically insulatingmaterial such as Dow Corning 993, a silicone varnish manufactured by theDow Corning Corporation, Midland, Mich, to saturate the fiber glasssleeves thoroughly and form a slight coatin I thereover. Afterpermitting the fiber glass sleeves to air-dry at room temperature forone-half hour to a point where the saturated varnish is in a tackystate, the resistor is inserted into the cylindrical opening of themetal housing, the diameter of the opening being such that the resistorwith the sleeves assembled thereon and saturated as described will fitsnugly and occupy substantially the entire space within the opening,following which the resistor is baked at a temperature of 250 C. forabout four hours to drive off every particle of air from the mass ofinsulating material composing the cylindrical sleeves and the saturatingmaterial surrounding the resistor and to cure the saturating material,so that the space between the resistor and metal housing is entirelyfree from air and i filled solidly with insulating material such asglass and with the saturating material.

The ends of the resistor are then coated or sealed with silicone varnishor other suitable electrically insulating material, as indicated at M,which surrounds the conductors 3 and occupies the area over the ends ofthe resistor between the conductors 3 and the surrounding metal housing,which projects slightly beyond the ends of the resistor and surroundinginsulating sleeves as shown clearly in Fig. 3.

It will be understood that the opening that is formed in the metalhousing is of a diameter to accommodate properly the resistor andsurrounding insulating sleeves with the plastic material saturating thelatter so that when the resistor unit is inserted into the openingwithin the metal housing, it fits tightly therein, and the sleeves l and9 are selected of a size so as to fit closely around the resistor and tofill the space between the cylindrical surface of the resistor and thesurrounding surface of the metal housing.

Beneath the cylindrical opening that receives the resistor, the metalhOllSing includes a relatively thick base portion I2, the sides of whichare substantially parallel as shown. The base 62 preferably has a widthat least as great as the width of the housing at its upper portion wherethe resistor is secured in the cylindrical opening. and the base orlower portion l2 of the housing preferably terminates in lateral flangesl3 provided with openings I4 to receive screws 15 for attaching thehousing to a metal chassis or support l6.

With this arrangement, a resistor having an actual length ofapproximately 1'' and a maximum diameter of approximately will withstandelectrical loads that otherwise would require resistor of approximatelyfive times the size. A resistor such as shown, without the metalhousins, will reach a temperature of 250 C. when carrying a 5 wattcurrent load, and it is not possible with resistors as heretoforeconstructed to mount a resistor on a metal chassis in electronicinstallations, but the resistor must be suspended by brackets, whereaswith the present structure, the resistor can be mounted directly on ametal plate or support, and a current load of 10 watts produces atemperature on the metal housing of only 40 C. as compared with asimilar resistor without the metal housing producing a temperature of250 C. when carrying a load of 5 watts. With the present structure, acurrent load of 20 watts produces a temperature in the housin of onlyC., and a current load of 30 watts produces a temperature in the housingof only 119 C.

With resistors as heretofore constructed, a rated current load of 30watts has required a resistor unit 3" long and /8" in diameter, whereasthe present structure occupies a space approximately one-fourth thatsize and with a current load of 30 watts produces a high temperature onthe outside of the housing of only 119 C., compared with 250 C. for a 30watt unit, free air rating of conventional type, operated at full load.The structure therefore possesses superiorities and practical advantagesthat have not been possible with any of the resistor constructionsheretofore available.

The structure may be constructed of difierent sizes for varyingcapacities and with the resistor herein shown for a 5 watt rating, theopening in the metal housing has a diameter of and the metal wall abovethe opening a thickness of .07". The base below the opening is .483"wide at the top of the flanges and .984" wide at the bottom of theflanges. the flanges are 3% thick and the housing has an overall lengthof 1%", These are successful dimensions for a 5 watt unit and for a 10watt unit, the holein the housing has a diameter of 5%"; the width ofthe base is .546" at the top of the flanges and 1.047 at the bottom ofthe flanges, and the overall length is 1.802", the other dimensionsremaining the same as for the 5 watt unit.

With a 5 watt unit such as described above, a current of 80.2 watts wasrequired to raise the internal temperature of the resistor to 251 C.whereas the same unit without the metal housing rose to a temperature of250 C. with only 5 watts of current, and 15 watts would render theresistor useless.

While the invention has been described with reference to the particularmethod and structure shown and described, this appliction is notconfined to the details herein set forth and this application isintended to cover such modifications and departures as may come withinthe purposes of the invention or the scope of the following claims.

I claim:

1. In combination, a rigid metal housing having an upper portion whichhas a longitudinal opening extending therethrough, a high-voltageelectrical resistor having conductor wires extending centrally from theends thereof, said resistor being mounted within said opening with theconductor wires extending centrally beyond the ends of said opening,said opening being of a size to fit closely about the resistor and thewall of said housing which surrounds said opening being of substantialthickness and entirely surrounding said opening, said housing having abase integral therewith for attachment to a support, said base having agreater thickness than said wall and being of a width throughoutsubstantially as great as the width of said upper portion, and a body ofelectrically insulating material arranged around the resistor between itand the housing and entir'ely filling the space between the resistor andthe housing and surrounding the conductor wires at the ends thereofadjacent to the resistor and covering the ends of the resistor.

2. In combination, a. rigid metal housing having a longitudinallyextending cylindrical opening therethrough, a high-voltage electricalresistor of the type in which a length of wire is wound on a hollowcylindrical insulating body which has metallic caps at its opposite endsclosing the ends of said insulating body and to which the opposite ends,respectively, of the wire are secured and which has conductor wiresextending axially outwardly from the caps, said resistor beingmounted-within the opening of the housing with its conductor wiresextending outwardly beyond the ends of the opening. said opening beingof a diameter to fit closely about the resistor, the wall of saidhousing entirely surrounding the resistor and being of substantialthickness, said housing having an integral one-piece base below saidopening for attachment to a support, said base having a width throughoutsubstantially as great as the diameter of said opening and terminatingin oppositely extending lateral flanges, and a body of electricallyinsulating material arranged around the resistor and between it and thehousing and entirely filling the space between the resistor and thehousing and surrounding the conductor wires and covering the caps andsealing the ends of the opening.

3. In combination, a rigid metal housing having a longitudinallyextending cylindrical opening therethrough, a high-voltage electricalresistor of the type in which a length of wire is wound on a hollowcylindrical insulating body which has metallic caps at its opposite endsclosing the ends of said insulating body and to which the opposite ends,respectively, of the wire are secured and which has conductor wiresextending axially outwardly from the caps, said resistor being mountedwithin the opening of the housing with its conductor wires extendingoutwardly beyond the ends of said opening, a cylindrical envelope ofelectrically insulating porous material arranged about the resistorbetween it and the housing, and a body of insulating material aroundsaid envelope and impregnated into said envelope and acting with saidenvelope to fill entirely the space between the resistor and thehousing, said housing having a base integral with it below said opening,said base having a width throughout substantially as great as thediameter of said opening.

MELVIN A. 'I'HOM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,092,790 Garrison Apr. 7, 19141,124,849 Brush Jan. 12, 1915 1,434,225 Rice Oct. 31, 1922 1,494,939Abbott May 20, 1924 1,699,898 Lightfoot Jan. 22, 1929 2,146,509 MucherFeb. 7, 1939 2,218,204 Marsten Oct. 15, 1940 2,227,931 Greenleaf Jan. 7,1941 2,378,772 Hummel June 19, 1945 2,387,829 Burnham Oct. 30, 1945FOREIGN PATENTS Number Country Date 342,223 Great Britain Jan. 29, 1931

